Just wondering if there are any 3rd party exterior storage options for Class B's such as the Roadtrek 190? I was thinking of something along the lines of a Thule roof box or even something mounted to the back fender or door. Just checking my options to maximize how much I can carry.

Personally, I don't think adding an exterior storage on top since the top is already very tall. It might cause you problems, especially if you're going to be camping in a place where there's a lot of trees. I'd suggest getting a tailgate rack instead. You can attach this to the rear hitch and then mount a storage box there.

The irony of adding an exterior storage option is that you end up with just the same amount of space. At least, that's how I see it since you need to put the exterior storage at the rear, you'll need to find a place for your spare tire and other stuff. So that would mean that the back end of your class B will be occupied with this stuff.